Glass fiber reinforced gypsum and glass fiber reinforced cement are known. According to the terminology used herein, glass fiber reinforced substances are compound materials, that is materials produced by embedding a first substance present in the form of particles, whiskers, fibers, laminae or unoriented fibers in a second substance--the matrix. Cement, for example, is a compound material used in the construction industry. The use of such compound materials in laminates for the production of molds, models and tools has not been known.
A significant and economically important sector in the construction of vehicles, ships and particularly aircraft is known to be the construction of molds. Molds and tools having specific characteristics are required today for the production of more and larger vehicle parts. In addition to metals, e.g. electroplated nickel, woven structures of glass or carbon fiber reinforced epoxy resins are used for this purpose. Originals and copied models are frequently produced from epoxy resins reinforced with woven fibers or from unsaturated polyester resins reinforced with woven fibers. Like the molds, these models have a high surface quality and can be produced much more cost effectively than metal models.
It is also known that plastic molds made of epoxy resins or unsaturated polyester resins reinforced with glass fiber fabrics can also be used for the production of smaller models employing the wet pressing, injection molding and vacuum drawing methods, with light-weight molds being provided with reinforcing ribs. If high pressures are employed, the molds are lined with more stable materials, e.g. mixtures of epoxy resin and quartz sand. Compared to steel molds, plastic molds are more economical and are an appropriate supplement for the economical development of prototypes.
European Patent Application No. 124,801 and German Patent No. 77,796 disclose the production of molds based on .beta.-calcium sulfate hemihydrate and/or cement. However, it is characteristic for these and other prior art processes that all the molds produced are porous, they absorb moisture and are gas permeable. The mechanical characteristics of such molds are not sufficient for their use in vehicle and aircraft construction. These molds cannot be used even if particles, e.g. whiskers, glass fibers and the like, are embedded in the pourable molding compositions, which still produce porous compound substances on a gypsum or cement basis.
According to British Patent No. 1,119,585, on a cement base are produced in such a manner that initially a liquid resin layer, composed of epoxy resin and hardener is cooled in a mold to at least 30.degree. C. and then a cement containing layer is poured onto the viscous resin layer. It is important in this process that both layers harden at the same time and are thereby bonded firmly with one another. Mold bodies produced in this manner have a surface layer of synthetic resin on their cement containing base layer. However, this process is also unsuitable for the production of molds for large structural components or models.
Gypsum or cement bound molding compositions have therefore not previously been used to the same extent as the synthetic resin bound molding compositions in the construction of tools, molds and models.
Gypsum molds have not previously been used in this field because their strength is too low, due to their high porosity, and because their expansion is too high. The result is that their retention of dimensions and their moldability have not been sufficient.